Simpson, 29, thinks United's form will either work for or against Leicester - but much will depend on the opening exchanges.
He said: "You can look at it in different ways. They won't want to lose again so they may be more hungry and more determined especially with them being at home.
"If we start well they might feel the pressure from their fans or the players might not have as much confidence.
"Ibrahimovic is a quality player and he's scored goals everywhere he has been. It's not just his football, it's the aura and everything that comes with him.
"United have got a load of top players and we need to defend as we know we can defend."